球磨态La-Y-Mg-Ni合金的显微组织和储氢性能

为了提高La-Y-Mg-Ni合金的储氢性能,通过对铸态合金进行5~30 h的球磨,制备具有非晶和纳米晶结构的La_(1.7)Y_(0.3)Mg_(16)Ni合金,并研究显微组织对储氢性能的影响及其机理。结果表明,随着球磨时间的延长,合金的结晶度、晶粒尺寸和粒径减小,非晶相增加。纳米晶相和非晶相的双重调节作用导致储氢动力学性能先加快,后减慢。经过15 h球磨的合金具有最好的吸、放氢动力学特性,在373 K下10 min内可以吸收3.10%(质量分数)的氢气,其放氢活化能最低,为71.2 k J/mol。球磨不同时间的合金的热力学性能的变化很小,球磨15 h后合金的放氢焓变最低,为72.9 k J/mol。

Electrochemical performances of as-cast and annealed La_(0.8-x)Nd_xMg_(0.2)Ni_(3.35)Al_(0.1)Si_0.05(x=0-0.4) alloys applied to Ni/metal hydride (MH) battery

The La-Mg-Ni-based A2B7-type Lao.8_xNdx Mgo.2Ni3.35Alo.lSio.o5 （x = 0, 0.1, 0.2, 0.3, and 0.4） electrode alloys were prepared by casting and annealing. The influence of the partial substitution of Nd for La on the structure and electrochemical performances of the alloys was investigated. The structural analysis of X-ray diffraction and scanning electron microscopy reveals that the experimental alloys consist of two major phases： （La,Mg）2Ni7 with the hexagonal Ce2Ni7-type structure and LaNi5 with the hexagonal CaCus-type structure as well as some residual phases of LaNi3 and NdNis. The electrochemical measurements indicate that an evident change of the electrochemical performance of the alloys is associated with the substitution of Nd for La. The discharge capacity of the alloy first increases then decreases with the growing Nd content, whereas their cycle stability clearly grows all the time. Furthermore, the measurements of the high rate discharge ability, the limiting current density, and hydrogen diffusion coefficient all demonstrate that the electrochemical kinetic properties of the alloy electrodes first augment then decline with the rising amount of Nd substitution.

Electrochemical hydrogen storage performance of as-cast and as-spun RE-Mg-Ni-Co-Al-based alloys applied to Ni/MH battery

The La-Mg-Ni-Co-Al-based AB2-type La0.8-xCe0.2YxMgNi3.4Co0.4Al0.1(x=0,0.05,0.1,0.15,0.2)alloys were prepared via melt spinning.The analyses of the X-ray diffraction(XRD)and scanning electron microscopy(SEM)proved that the experimental alloys contain the main phase LaMgNi4 and the second phase LaNi5.Increasing Y content and spinning rate lead to grain refinement and obvious change of the phase abundance without changing phase composition.Y substitution for La and melt spinning make the life-span of the alloys improved remarkably,which is attributed to the improvement of anti-oxidation,anti-pulverization and anti-corrosion abilities.In addition,the discharge capacity visibly decreases with increasing the Y content,while it firstly increases and then decreases with increasing spinning rate.The electrochemical kinetics increases to the optimum performance and then reduces with increasing spinning rate.Moreover,all the alloys achieve to the highest discharge capacities just at the initial cycle without activation.

Hydriding and dehydriding kinetics of melt spun nanocrystalline Mg20Ni10-xCux (x = 0-4) alloys

The nanocrystalline Mg2Ni-type electrode alloys with nominal compositions of Mg20Ni10-xCux (x = 0, 1, 2, 3, 4) were synthesized by melt-spinning technique. The microstructures of the alloys were characterized by XRD, SEM and HRTEM. The hydrogen absorption and desorption kinet-ics of the alloys were measured using an auto-matically controlled Sieverts apparatus. The re- sults show that all the as-spun alloys hold ty- pical nanocrystalline structure. The substitution of Cu for Ni does not change the major phase Mg2Ni but it leads to the formation of the sec-ondary phase Mg2Cu. The hydrogen absorption capacity of the alloys first increases and then decreases with rising Cu content, but the hy-drogen desorption capacity of the alloys mono- tonously grows with increasing Cu content. The melt spinning significantly improves the hydro- genation and dehydrogenation capacities and kinetics of the alloys.

Impacts of Melt Spinning and Element Substitution on Electrochemical Characteristics of the La–Mg–Ni-based A₂B₇-Type Alloys

The partial substitution of Zr for La has been performed in order to ameliorate the electrochemical hydrogen storage performances of La–Mg–Ni based A2B7-type electrode alloys. The melt spinning technology was used to prepare the La0.75-xZrxMg0.25Ni3.2Co0.2Al0.1 (x=0, 0.05, 0.1, 0.15, 0.2) electrode alloys. The impacts of the melt spinning and the substituting La with Zr on the structures and the electrochemical hydrogen storage characteristics of the alloys were systemically investigated. The analysis of XRD and TEM reveals that the as-cast and spun alloys have a multiphase structure, composing of two main phases (La, Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2. The electrochemical measurement indicates that both the substitution of Zr for La and the melt spinning ameliorate the electrochemical cycle stability of the alloys dramatically. Furthermore, the high rate discharge ability (HRD) of the as-spun (10 m/s) alloys notably declines with growing the amount of Zr substitution, while it first augments and then falls for the (x=0.1) alloy with rising the spinning rate.

Hydrogen storage thermodynamics and kinetics of as-cast Ce-Mg-Ni-based alloy

The reaction kinetics of alloys based on magnesium are known to be greatly improved by the partial substitution of Mg with rare earths and transition metals,particularly Ni.The enhanced superficial hydrogen dissociation rate,the weakened Mg-H bond and the lower activation energy following element replacement are thought to be related to the better performance.The experimental alloys Ce5Mg_(95-x)Ni_(x)(x=5,10,15)were smelted by the vacuum induction melting.The phase transformation and structural evolution of experimental alloys before and after reaction with hydrogen were char-acterized by X-ray diffraction,scanning electron microscopy and transmission electron microscopy.The cast specimens contain CeMg_(12),Mg and Mg_(2)Ni phases,and the increase in Ni content results in an obvious growth of Mg_(2)Ni phase.The isothermal and non-isothermal hydrogenation and dehydrogenation kinetics of the experimental specimens were investi-gated using the Sievert apparatus,differential scanning calorimetry and thermal gravimetric analyzer.The activation energy may be calculated using the Arrhenius and Kissinger equations.The experimental alloys have been shown to have good activation properties,with a reversible hydriding and dehydriding capacities of around 5.0 wt.%in the first cycle.The initial dehydrogenation temperature of MgH_(2) decreases from 557.5 to 537.7 K with changing Ni content from 5 to 15 at.%.The dehydrogenation activation energy also reduces from 77.09 to 62.96 kJ/mol,which explains the improved hydrogen storage performance caused by Ni substitution.It can be shown that the impact of Ni on the decomposition enthalpy of MgH_(2) is quite modest,with the absolute enthalpy(ΔHr)only decreasing from 78.48 to 76.15 kJ/mol.

Research and application of Ti-Mn-based hydrogen storage alloys

Ti–Mn-based hydrogen storage alloys are considered to be one of the most promising hydrogen storage alloys for proton exchange membrane fuel cell applications,because of their good hydrogen absorption and desorption kinetics,low price,good activation performance,possession of high electrochemical capacity,and good cycling performance.The structure,performance characteristics,crystal structure of hydrides,development and application status of Ti–Mn-based hydrogen storage alloys were reviewed,and the methods to improve Ti–Mn-based hydrogen storage alloys were discussed:optimization of the preparation process,element substitution,and surface treatment.(1)In the study of the alloy preparation process,it was found that the use of the annealing process can significantly improve the high rate discharge performance,and cycling stability performance,increasing the maximum discharge capacity of the alloy electrode.In addition,using vacuum plasma spraying to prepare the electrode has better cycling stability and kinetic performance.(2)In element substitution,the effects of using Zr elements to partially replace Ti and Mn with Cr,V,Mo,and Fe on the hydrogen storage properties of Ti–Mn-based alloys were investigated.(3)In the study of surface treatment,palladium was plated on the surface of TiMn_(1.5) alloy by chemical deposition,and the strong affinity of palladium for hydrogen accelerated the cleavage of hydrogen molecules,which significantly improved the hydrogen absorption kinetics of TiMn_(1.5) alloy.Meanwhile,a new binary alloy system was formed by adding TiMn_(2) to MgH_(2),and it was shown that the addition of TiMn_(2) significantly improved the hydrogen absorption/desorption kinetics of the MgH_(2) alloy.Finally,the prospect of the application of Ti–Mn-based hydrogen storage alloys is presented,and the insight of further development of the alloy is offered.

Research progress in Mg-based hydrogen storage alloys

Magnesium and magnesium-based alloy hydrides remain attractive hydrogen storage materials owing to high hydrogen capacity and rich reserves in the earth＇s crust. A high stability of hydride and sluggish hydriding/dehydriding kinetics at practical temperatures for the materials drove researchers into alloying with other elements, using different preparation techniques, using catalyst and thin film hydride to improve the hydrogen absorption/desorption properties. In this review, the development of these approaches and their effects on the thermodynamic and kinetics properties of magnesium and magnesium-based alloy hydrides were descript in details.

The electrochemical hydrogen storage performances of Si-added La–Mg–Ni–Co-based A_2B_7-type electrode alloys

In order to improve the electrochemical cycle stability of the RE–Mg–Ni-based A2B7-type electrode alloys, a small amount of Si has been added into the alloys.The casting and annealing technologies were adopted to fabricate the La0.8Mg0.2Ni3.3Co0.2Six(x = 0–0.2) electrode alloys. The impacts of the addition of Si and annealing treatment on the structures and electrochemical performances of the alloys were investigated systematically. The results obtained by XRD and SEM show that all the as-cast and annealed alloys are of a multiphase structure, involving two main phases(La, Mg)2Ni7and La Ni5 as well as a residual phase La Ni3. Both adding Si and the annealing treatment lead to an evident change in the phase abundance and cell parameters of(La, Mg)2Ni7and La Ni5 major phases of the alloy without altering its main phase component. Moreover, the annealing treatment has the composition of the alloy distributed more homogeneously overall and simultaneously causes the grain of the alloy to be coarsened obviously. The electrochemical measurements indicate that adding Si and the annealing treatment give a significant rise to the influence on the electrochemical performances of the alloys. In brief, the cycle stability of the as-cast and annealed alloys evidently increases with the rising of Si content, while their discharge capacities obviously decrease under the same circumstances. Furthermore, the electrochemical kineticproperties of the electrode alloys, including the high rate discharge ability, the limiting current density(IL), hydrogen diffusion coefficient(D), and the charge-transfer resistance, first augment and then decline with the rising of Si content. Similarly, it is found that the above-mentioned electrochemical properties first mount up and then go down with the rising annealing temperature.

Microstructure and damping properties of MnCuNiFeCe alloy

Mn-Cu alloys could exhibit high damping ability and excellent mechanical properties after proper heat treatment. In order to reduce the influence of impurity elements on damping capacity of Mn-Cu alloys, rare ele- ment cerium （Ce） was added into MnCuNiFe alloys. It is indicated that the contents of C, S and Si which have adverse effects on the damping capacity decrease and the grains are refined with the Ce content increasing. The microstructure of the MnCuNiFeCe alloy was investigated by X-ray diffraction （XRD）, scanning electron microscope （SEM） and transmission electron microscopy （TEM）. The damping ability （tane） of the alloy was characterized by dynamical mechanical analyzer （DMA）. It is found that the damping ability （tane） retains a very high level which is all above 0.05 from the temperature of -50 to 75 ℃ with the addition of Ce element. It is expected that the Ce alloying MnCuNiFe alloy with refined grains could find wide applications in the field of industry.

The electrochemical hydrogen storage characteristics of as-spun nanocrystalline and amorphous Mg_(20)Ni_(10-x)M_x(M=Cu, Co, Mn;x=0–4) alloys

In this paper, we comprehensively investigate the influences of M（M=Cu, Co, Mn） substitution for Ni on the structures and electrochemical hydrogen storage characteristics of the nanocrystalline and amorphous Mg20Ni10-xMx（M=Cu, Co, Mn; x = 0–4） alloys prepared by melt spinning. The as-spun（M=None, Cu） alloys display an entire nanocrystalline structure, whereas the as-spun（M=Co, Mn） alloys hold a mixed structure of both nanocrystalline and amorphous when x = 4（M content）. These results indicate that the substitution of M（M=Co, Mn） for Ni facilitates the glass formation in Mg2Ni-type alloy. All the as-spun alloys have the Mg2 Ni major phase, but M（M=Co, Mn） substitution brings on some secondary phases,such as Mg Co2, Mg phases for M=Co, and Mn Ni, Mg phases for M=Mn. The substitution of M（M=Cu, Co, Mn）for Ni also makes a positive contribution to the cycle stability of the alloys in the following orders：（M=Cu） [（M=Co） [（M=Mn） for x = 1 and（M=Co） [（M=Mn）[（M=Cu） for x = 2–4. Meanwhile, it notably enhances the discharge capacity of the alloys in the sequence of（M=Co） [（M=Mn） [（M=Cu）. As for the high rate discharge ability, it visibly upgrades with the growing of M content for（M=Cu, Co）, while it grows at first and then declines for（M=Mn）.

Structures and hydrogen storage properties of RE-Mg-Ni-Mn-based AB2-type alloys prepared by casting and melt spinning

To ameliorate the electrochemical hydrogen storage properties of RE-Mg-Ni-Mn-based AB2-type electrode alloys,La element was partially substituted by Ce,and La1-xCexMgNi3.5Mn0.5(x=0,0.1,0.2,0.3,0.4)alloys were fabricated by casting and melt spinning.The effects of Ce content on structures and electrochemical hydrogen storage properties of prepared alloys were studied in detail.Results show that the experimental alloys consist of LaMgNi4 and LaNi5 phases.The variation of Ce content,instead of changing phase composition,results in an obvious phase abundance change in the alloys,namely the amount of LaMgNi4 and LaNi5 phases,respectively,increases and decreases with Ce content growing.Moreover,the partial substitution of Ce for La leads to that the lattice keeps constant,cell volumes clearly decreases and the alloy grains are markedly refined.The electrochemical measurements reveal that the as-cast and as-spun alloys obtain the maximum discharge capacities at the first cycling without any activation needed.With Ce content increasing,the discharge capacity of as-cast alloys visibly decreases.By contrast,the as-spun alloys have the maximum discharge capacity value.The substitution of Ce for La dramatically promotes the cycle stability.Moreover,the electrochemical kinetic performances of as-cast and asspun alloys first increase and then decrease with Ce content increasing.

Electrochemical hydrogen storage behaviors of as-cast and spun RE-Mg-Ni-Co-Al-based AB2-type alloys applied to Ni-MH battery

Preparation of La-Mg-Ni-Co-Al-based AB2-type alloys La0.8-xCe0.2YxMgNi3.4Co0.4Al0.1(x=0,0.05,0.10,0.15,0.20)was performed using melt spinning technology.The influences of spun rate and Y content on structures and electrochemical hydrogen storage characteristics were studied.The base phase LaMgNi4 and the lesser phase LaNis were detected by X-ray diffraction(XRD)and scanning electron microscope(SEM).The variations of spinning rate and Y content cause an obvious change in phase content,but without altering phase composition,namely,with spinning rate and Y content growing,LaMgNi4 phase content augments while LaNi5 content declines.Furthermore,melt spinning and the replacing La by Y refine the grains dramatically.The electrochemical tests show a favorable activation capability of the two kinds of alloys,and the maximum discharge capacities are achieved during the first cycle.Discharge capacity firstly increases and subsequently decreases with spinning rate rising,while cycle stability is ameliorated and discharge capacity decreases with Y addition increasing.It is found that the amelioration of cycle stability is due to the enhancement of anti-pulverization,anti-corrosion and antioxidation abilities by both replacement of La with Y and melt spinning.Moreover,with the increase of Y addition and/or spinning rate,the electrochemical kinetics that contain charge transfer rate,limiting current density(IL),hydrogen diffusion coefficient(D)and the high rate discharge ability(HRD)firstly augment and then reduce.

Self-lubricating CrVN Coating Strengthened via Multilayering with VN

To improve the mechanical properties of self-lubricating chromium vanadium nitride （CrVN） coatings, va- nadium nitride （VN） is combined with CrVN to form multilayered CrVN/VN coatings through an in-line magnetron sputtering system. The strengthening effect of the period thickness on the mechanical and tribological properties is studied. X-ray diffractometer, low-angle X-ray reflectivity, scanning electron microscopy, atomic force microscopy, electron probe micro-analyzer and X-ray photoelectron spectroscopy are employed to characterize the microstructures and chemical composition. Nanoindentation and ball-on-disc tribo-tester are used in characterization of the mechanical and tribological properties. The CrVN/VN multilayer coatings demonstrate good lubrication property with coefficient of friction down to 0.23. Multilayering with VN, the hardness of CrVN jumps to 27.6 GPa with period thickness of 6 nm, which has an improvement of 5.1 GPa compared with that of 22.5 GPa from rule-of-mixture.

Microstructure,mechanical and corrosion properties of TiN/Ni nanomultilayered films

Nanomultilayered TiN/Ni thin films with different bilayer periods(57.8-99.7 nm) and Ni single-layer thickness(3.9-19.2 nm) were prepared by alternatively sputtering Ti and Ni targets in N2 gas atmosphere.The micros tructure,mechanical and corrosion properties of the multilayer films were investigated by X-ray diffraction(XRD),field emission scanning electron microscopy(FESEM),X-ray photoelectron spectroscopy(XPS),nanoindenter and electrochemical technologies.The multilayer films are fine with a mean grain size of ~8-9 nm independent of the bilayer period.However,the smoothness and compactness seem to decrease with the bilayer period increasing.The hardness(H) and elastic modulus(E) of the multilayer films gradually decrease as the bilayer period increases,and the multilayer film with bilayer period of 57.8 nm exhibits higher H,ratios of(H/E^*and H^3/E^*2)(E^*is effective Young’s modulus)than the monolithic TiN film and the other multilayers.The multilayer films exhibit an obvious passivation phenomenon in 10% H2SO4 solution,and the passive current and corrosion current densities decrease,whereas the corrosion potential increases when the bilayer period or Ni single-layer thickness decreases.It is found that the passivating behavior and corrosion potential of the multilayers are more sensitive to Ni single-layer thickness than the bilayer period.More corrosion pits and lamellar flaking could be found on the films with larger bilayer period or Ni single-layer thickness.

Research progress of TiFe-based hydrogen storage alloys

After being activated,TiFe alloys are widely concerned for their high hydrogen storage density due to their large reversible absorption and desorption capacity of hydrogen at room temperature,low price,abundant resources,moderate hydride decomposition pressure,and good hydrogen absorption and desorption kinetic performance.Meanwhile,TiFe alloys can be used as anode materials for secondary batteries,catalysts for hydrogenation,and storage media for thermal,solar,and wind energy,which has wide industrial application prospects.However,TiFe alloys have disadvantages such as difficult activation,easy toxicity,and large hysteresis.This review introduces the current research status and performance characteristics of TiFe-based hydrogen storage alloys,the phase structure,hydride phase structure,kinetic and thermodynamic models of TiFe alloys,as well as the application prospects of TiFe-based hydrogen storage alloys in practical production and the ways to improve their hydrogen storage performance,and presents the views on the future research priorities and development directions of TiFe-based hydrogen storage alloys.

Structures and electrochemical performances of as-cast and spun RE-Mg-Ni-Mn-based alloys applied to Ni-MH battery

The RE-Mg-Ni-Mn-based AB2-type La（1-x）CexMgNi（3.5）Mn（0.5）（ x = 0- 0. 4） alloys were prepared by spinning treatment. For obtaining the optimum performance,the effects of Ce content and spinning rate on the hydrogen storage performance of the alloys were studied systematically. The results show that the variations of the spinning rate and Ce content result in noteworthy changes of the phase content without altering phase composition of the alloys. Specifically,the LaMgNi4 phase increases and LaNi5 phase decreases when increasing the spinning rate and Ce content. Furthermore,the crystalline grains of Cecontaining alloys prepared by spinning treatment are remarkably refined. The alloys own superior electrochemical performance. All alloys reach the optimal discharge capacity at the initial cycle. Increasing Ce content and spinning rate lead the discharge capacity and electrochemical kinetics rise to an optimal value and then start to reduce. Meanwhile,the electrochemical cycle stability is also improved,which is ascribed to the great enhancement of anti-pulverization and anti-corrosion abilities resulting from the spinning treatment and the substitution of Ce for La.

Synthesis and microwave absorption property of nanostructured Ketjen black/Fe_(3)O_(4) core/shell particles

Nanostructured Ketjen black/Fe_(3)O_(4) core/shell particles have been prepared through a simple one-step hydrothermal method.The microstructure analysis shows that the assynthesized composite particles display a typical core/shell structure:the Ketjen black is playing as the core,while a large number of Fe_(3)O_(4) nanoparticles are uniformly attaching to the surface of the Ketjen black and forming the shell.The investigation of the magnetic properties of the nanostructured Ketjen black/Fe_(3)O_(4) core/shell materials reveals that the as-synthesized composite is a typical soft ferromagnetism material.The 40 wt%Ketjen black/Fe_(3)O_(4)-paraffin composites exhibit an excellent reflection loss value of-64.21 dB at a thickness of 2.00 mm,and the broadest effective bandwidth of 4.17 GHz at a thickness of1.50 mm.This work provides a brand-new type of magnetic carbon nanoparticles,defined as Ketjen black/Fe_(3)O_(4)core/shell particles,which are an excellent candidate for high-perform ance electromagnetic wave absorber materials.

Gaseous and electrochemical hydrogen storage behaviors of nanocrystalline and amorphous Nd-added Mg_2Ni-type alloys

Melt spinning technology was used to prepare the Mg2Ni-type(Mg24Ni10Cu2)100-xNdx(x = 0, 5, 10, 15,20) alloys in order to obtain a nanocrystalline and amorphous structure.The effects of the spinning rate on the structures and gaseous and electrochemical hydrogen storage behaviors of the alloys were investigated.The analysis of X-ray diffraction(XRD), transmission electron microscope(TEM), and scanning electron microscope(SEM) linked with energy-dispersive spectroscopy(EDS)reveals that all the as-cast alloys hold a multiphase structure, involving the main phase Mg2 Ni and some secondary phases such as Mg6 Ni, Nd5Mg41, and Nd Ni.The as-spun Nd-free alloy displays an entire nanocrystalline structure,whereas the as-spun Nd-added alloys hold a nanocrystalline and amorphous structure, and the amorphization degree visibly increases with the spinning rate increasing.The melt spinning ameliorates the hydrogen storage performances of the alloys dramatically.When the spinning rate rises from 0(the as-cast was defined as the spinning rate of 0 m s-1) to 40 m s-1, the discharge capacity increases from 86.4 to 452.8 m Ah g-1, the S20(the capacity maintain rate at 20 th cycle) value increases from53.2 % to 89.7 %, the hydrogen absorption saturation ratio(Ra5, a ratio of the hydrogen absorption quantity in 5 min to the saturated hydrogen absorption capacity) increases from36.9 % to 91.5 %, and the hydrogen desorption ratio(Rd10,a ratio of the hydrogen desorption quantity in 10 min to the saturated hydrogen absorption capacity) increases from16.4 % to 47.7 % for the(x = 10) alloy, respectively.

Novel dye-sensitized solar cell architecture using TiO2-coated Ag nanowires array as photoanode

With the aim of reducing series resistance and increasing dye loading,novel dye-sensitized solar cell architecture was designed with TiO2 nanoparticle-coated Ag nanowires array as the photoanode.Ag nanowire array was prepared by anodic aluminum oxide (AAO) templateassisted electrochemical deposition route.Then,Ag nanowires were coated by TiO2 nanoparticles in hydrothermal process.The structures of the photoanode were characterized by field emission scanning electron microscopy (FESEM).Ag nanowires are covered by a layer of very fine nanoparticles with a diameter of less than 5 nm.X-ray diffraction (XRD) and selected-area electron diffraction (SAED) show that Ag nanowires have a strong preferred orientation in (220) direction and the TiO2 coating layer is a polycrystalline structure.With this photoanode,3.2 % conversion efficiency is achieved for the cell sensitized with N3 dye.